While Ziegler-Natta catalysts are a mainstay for polyolefin manufacture, single-site (metallocene and non-metallocene) catalysts represent the industry's future. These catalysts are often more reactive than Ziegler-Natta catalysts, and they produce polymers with improved physical properties. The improved properties include controlled molecular weight distribution, reduced low molecular weight extractables, enhanced incorporation of α-olefin comonomers, lower polymer density, controlled content and distribution of long-chain branching, and modified melt rheology and relaxation characteristics.
Traditional metallocenes incorporate one or more cyclopentadienyl (Cp) or Cp-like anionic ligands such as indenyl, fluorenyl, or the like, that donate pi-electrons to the transition metal. Non-metallocene single-site catalysts, including ones that capitalize on the chelate effect, have evolved more recently. Examples are the bidentate 8-quinolinoxy or 2-pyridinoxy complexes of Nagy et al. (see U.S. Pat. No. 5,637,660), the late transition metal bisimines of Brookhart et al. (see Chem. Rev. 100 (2000) 1169), and the diethylenetriamine-based tridentate complexes of McConville et al. or Shrock et al. (e.g., U.S. Pat. Nos. 5,889,128 and 6,271,323).
In numerous recent examples, the bi- or tridentate complex incorporates a pyridyl ligand that bears a heteroatom β- or γ- to the 2-position of the pyridine ring. This heteroatom, typically nitrogen or oxygen, and the pyridyl nitrogen chelate the metal to form a five- or six-membered ring. For some examples, see U.S. Pat. Nos. 7,439,205; 7,423,101; 7,157,400; 6,653,417; and 6,103,657 and U.S. Pat. Appl. Publ. No. 2008/0177020. In some of these complexes, an aryl substituent at the 6-position of the pyridine ring is also available to interact with the metal through C—H activation to form a tridentate complex (see, e.g., U.S. Pat. Nos. 7,115,689; 6,953,764; 6,706,829). Unfortunately, some of these complexes are tricky to prepare, and they are most useful unsupported; our own attempts to prepare similar complexes and support them on silica, for example, met with mixed results.
Less frequently, quinoline-based bi- or tridentate complexes have been described (see, e.g., U.S. Pat. Nos. 7,253,133; 7,049,378; 6,939,969; 6,103,657; 5,637,660 and Organometallics 16 (1997) 3282). The quinoline complexes disclosed in the art lack an 8-anilino substituent, a 2-aryl substituent, or both, and/or they are not dianionic and tridentate.
New non-metallocene catalysts useful for making polyolefins continue to be of interest. In particular, tridentate complexes that can be readily synthesized from inexpensive reagents are needed. The complexes should not be useful only in homogeneous environments; a practical complex can be supported on silica and readily activated toward olefin polymerization with alumoxanes or boron-containing cocatalysts. Ideally, the catalysts have the potential to make ethylene copolymers having high or very high molecular weights and can be utilized in high-temperature solution polymerizations.